In group separation, before precipitating out group III metal ions as hydroxides, it is necessary to boil then solution of the salt mixture with a few drops of concentrated HNO3 is treated. This is do

Question

In group separation, before precipitating out group III metal ions as hydroxides, it is necessary to boil then solution of the salt mixture with a few drops of concentrated HNO3 is treated. This is done to convert:

Prashant Kotian · Accepted Answer

Correct answer: B. Step 1: Ferrous hydroxide, Fe(OH)2, has a much larger solubility product (Ksp ~ 8 x 10^-16) compared to ferric hydroxide, Fe(OH)3 (Ksp ~ 4 x 10^-38). Step 2: In the Group III analytical buffer (NH4Cl/NH4OH), the hydroxide ion concentration is suppressed and is too low to completely precipitate Fe2+ as Fe(OH)2, whereas it is sufficient to completely precipitate Fe3+. Step 3: Therefore, the solution is boiled with concentrated HNO3 (a strong oxidizing agent) to oxidize any Fe2+ present to Fe3+, ensuring complete precipitation in Group III. This corresponds to option (b).

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